The studies proposed in this application are an attempt to determine the influence membrane lipid composition has on survival of cells subjected to hyperthermia and radiation, either alone or in combination. In order to gain a greater insight into the mechanism of cytolethality of these two agents, cells in which the lipid composition of the membrane has been modified either by drugs or nutritionally in vivo and in vitro, will be used. In addition, drugs which increase fluidity of membranes will be employed. It is hoped that such studies will aid in elucidating the molecular mechanism(s) responsible for the enhanced cytocidal action of radiation in heat-treated cells, and thereby provide a rational basis for improving individual and combined radiation and heat therapy.